As manufacturing technology advances, semi-conductor integrated circuits (ICs) placed on a single chip become larger and denser. Due to long distribution paths for the power supply voltages so-called IR-drop may cause insufficient voltage supplied to some devices of the IC. Especially when an IC is operated in a high performance operating mode, IR-drop can be significant.
Measuring voltage drop and/or voltage excursion is a very common problem and many solutions exist. Further, since the chip area of an IC may be very large, the supply voltage may vary depending on the point of measurement. Furthermore, if the power consumption in a certain operating mode is relatively high, the impedance of the circuit may cause a significant drop of the local supply voltage too. This, in turn, may also influence the robustness of operation of the circuit besides other reasons which influence the robustness and reliability of the circuits, such as supply noise, substrate noise, temperature, switching activity and clock duty cycle. To detect and later on deal with these effects, monitoring and measuring means are known but some constrains limit the possibilities for proper measurement and monitoring: Feeding additional lines to the points of interest on the chip and performing measurement at the outside of the chip is not desirable. Firstly, this would waste chip area. Secondly, since additional lines may pick up signals that do not actually exist on the measurement points. Thirdly, such additional lines would require additional external pins. Furthermore, building a full-fetched Analog-to-Digital converter would cost too much IC area and pose additional power constraints.
US 2006/0214672 discloses preconditioning of a first signal and a second signal, the first signal being representative of the voltage of the power supply line being monitored and the second signal being representative of the voltage of a reference power supply line. Then, the preconditioned first signal and second signals are compared by a comparator circuitry. This requires presence of reference voltage and an additional supply line from the voltage source to the point of comparison.
WO 2006/114727 discloses an integrated circuit with a distributed supply voltage monitoring system in which a reference voltage is retrieved from the local supply voltage by averaging in a low pass filter and D/A converting the filtered signal.
Summarizing approaches in the prior art either supply the comparison circuitry with an external reference voltage, or generate a reference signal by some kind of signal processing such as averaging a local supply voltage present in the proximity of the comparison means. Disadvantages of these types of monitoring are the need for additional reference signal supply lines and/or comparison of the local supply voltage with a filtered value of the local supply voltage. However, the filtered voltage does not represent the supply voltage as fed to the circuit, but the supply voltage diminished by the IR-drop at that specific location.